Add a CKEditor5 plugin for Drupal 9.3+, Drupal 10

Official Drupal documentation for building a plugin:
https://www.drupal.org/docs/drupal-apis/ckeditor-5-api/overview

Official Drupal docs for rewriting a plugin:
https://www.drupal.org/docs/core-modules-and-themes/core-modules/ckedito...

Official CKEditor documentation for rewriting a plugin:
https://ckeditor.com/docs/ckeditor5/latest/installation/getting-started/...

Example module:
https://www.drupal.org/project/ckeditor5_dev

Blog posts on the topic:
https://evolvingweb.com/blog/porting-ckeditor-5-plugin-drupal-10
https://tech.axelerant.com/create-and-integrate-ckeditor-5-plugin-with-d...

A bare starting point - files from ckeditor5_dev copied & renamed to match.

One problem is that the ckeditor plugin doesn't want to work with shortcodes, so we might be stuck there.

Missed changes to one file.

This may not be possible, I don't see any reference to using shortcodes in ckeditor5.

minnur created a merge request which provides a new approach for this functionality with ckeditor 5 and would be a great addition:
https://git.drupalcode.org/project/video_filter/-/merge_requests/7

While I think the better long-term approach would be to migrate to the Media module and just use 3rd party oembed integration, this could be a short-term solution for sites that aren't using the Media system.

Next steps

Split out the ckeditor5 changes from merge request #7 into its own merge request as much of the unrelated changes are being handled as separate issues.

Also, now that there's test coverage (#3439443: Add useful functional test) we can finish this off to make sure it works as expected.